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Research Papers

Concurrent and Hierarchical Multiscale Analysis for Layer-Thickness Effects of Nanoscale Coatings on Interfacial Stress and Fracture Behavior

[+] Author and Article Information
Jinghong Fan1

 Mechanical Engineering, Alfred University, Alfred, NY 14802fanjing@alfred.edu

Long He, Ross J. Stewart

 Mechanical Engineering, Alfred University, Alfred, NY 14802

1

Corresponding author.

J. Eng. Mater. Technol 134(3), 031012 (May 07, 2012) (10 pages) doi:10.1115/1.4006498 History: Received October 17, 2011; Revised March 18, 2012; Published May 04, 2012; Online May 07, 2012

To investigate the effects of coating layer thickness on stress and the debonding behavior near the interface of coating layer and substrate, multiscale analysis is a must since molecular dynamics (MD) simulations can only be performed on models with thicknesses of about tens of nanometers on common computers, but the real thicknesses of such layers are around 300–1200 nm. In this work, generalized particle dynamics (GP) modeling for Al coated on Fe is first developed by using an atomistic domain near the layer interface and having high-scale particles far from that region to reduce degrees of freedom. Results show that the thicker coatings experience lower local average shearing stresses for a given shear strain. However, it is found that when the layer thickness reaches a large value, further increase of the layer thickness will not greatly benefit the reduction of the stress, thereby not increasing the allowable load. This trend is consistent with the simulation for Al2 O3 coated on Fe by a hierarchical multiscale analysis which is formulated by proposing a nanoscale-based key variable, Gdb , called debonding energy density. This variable, defined by the debonding energy per unit area, is used to characterize material bonding strength in realizing that failure originates from the atomistic and nanoscale. The difference and connection of this low-scale fracture variable, Gdb , with crack energy release rate, GIC , in traditional fracture mechanics is illustrated and how Gdb can be easily determined through atomistic simulation is exemplified. To make the new variable effective in engineering applications, Gdb is used as input to a macroscopic scale finite element model. The obtained layer-thickness effect directly confirms the existence of a critical thickness, predicted by the GP method. This work is an effort in developing material failure theory from lower scales where material fracture originates but with applications in continuum scale via both hierarchical and concurrent multiscale analyses.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Introducing two imaginary domains for a natural boundary between atomistic domain and the second-scale particle domain

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Figure 2

A two-scale GP simulation model for investigating behavior of Al/Fe coating system

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Figure 3

Interfacial shear stress versus applied shear strain for different thicknesses of the Al coating layer on the iron substrate

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Figure 4

Failure process versus applied strain, ɛZ , under tensile load perpendicular to the interface for the Al2 O3 -Fe system

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Figure 5

The normal stress, σz , versus the elongation (or Z-displacement between the top and bottom boundary) along the Z-direction

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Figure 6

Configuration energy versus applied strain, ɛZ , for the Al2 O3 /Fe coating system

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Figure 7

Configuration energy versus strain for the Al2 O3 /Fe coating system with interfacial crack

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Figure 8

Failure process versus applied strain, ɛZ , under tensile load perpendicular to the interface for Si3 N4 -Fe system

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Figure 9

A sketch of the hierarchical multiscale analysis for thin layer coatings

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Figure 10

Double cantilever beam design for FEA on coating layer thickness effects

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Figure 11

Stress-plastic strain curve of low carbon steel for coating substrate

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Figure 12

The critical applied force for interface failure of the Al2 O3 /steel system versus the coating layer thickness

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